Social networking sites which have been using to communicate and build interpersonal relationshipsbecome communities for sharing knowledge among individuals. Social network services (hereaftercalled SNS) enable individuals to globally share knowledge beyond among organizational employeesand business partners. Swift trust plays a critical role in diffusing knowledge sharing amongindividuals who met at first time in the SNS. Swift trust was introduced to explain a uniqueform of trust which is fragile, easily broken and resilient in temporary teams by Meyerson et al. (1996). In this paper, we defined the swift trust in SNS as a thin form of trust which ischaracterized as fragility and resilience based on weak ties among individuals who met at firsttime in SNS. This study aims to analyze mediating effects of swift trust between knowledgesharing and its antecedents in SNS. We proposed a structural equation model including knowledgesharing, personal characteristics and service characteristics as its antecedents, and swift trust. The research model involves reputation and altruismas personal characteristics and social presence,easy of use, and service usefulness as service characteristics. A total of eleven hypotheses werederived from the research model as follows:Hypothesis 1 (H1): Reputation is positively associated with swift trust in SNS. Hypothesis 2 (H2): Altruism is positively associated with swift trust in SNS. Hypothesis 3 (H3): Social presence is positively associated with swift trust in SNS. Hypothesis 4 (H4): Perceived easy of use is positively associated with swift trust in SNS. Hypothesis 5 (H5): Perceived service usefulness is positively associated with swift trust in SNS. Hypothesis 6 (H6): Swift trust is positively associated with knowledge sharing in SNS. Hypothesis 7a (H7a): Swift trust plays a role of mediation between reputation and knowledgesharing in SNS. Hypothesis 7b (H7b): Swift trust plays a role of mediation between altruism and knowledgesharing in SNS. Hypothesis 8a (H8a): Swift trust plays a role of mediation between social presence andknowledge sharing in SNS. Hypothesis 8b (H8b): Swift trust plays a role of mediation between perceived easy of use andknowledge sharing in SNS. Hypothesis 8b (H8b): Swift trust plays a role of mediation between perceived serviceusefulness and knowledge sharing in SNS. A total of 298 valid samples were collected from SNS users. All hypotheses except H2 and H7bwere supported. Reputation has a positive influence on swift trust. Reputation also indirectlyinfluences knowledge sharing through swift trust. Organizations operating social networkingsites need to facilitate SNS users to build trust by offering opportunities to enhance theirreputation to elicit their positive knowledge sharing. Service characteristics such as socialpresence, easy of use, and usefulness have a positive influence on swift trust, and also indirectlyinfluence knowledge sharing through swift trust. Swift trust has a mediating effect betweenservice characteristics and knowledge sharing. Organizations operating social networking sitescan facilitate knowledge sharing by allowing the establishment of higher swift trust throughenhancement of social presence, service usefulness, and easy of use. This study contributes to understanding of the mediating effect of swift trust on knowledgesharing in SNS and gives strategic guidelines to SNS operators. Further implications for theoryand practice were discussed in this study.